Rotary, electrical discharge machined dies (EDM dies) per se have been known for some time as evidenced, for example, by U.S. Pat. Nos. 3,542,993, 3,550,479 and 3,796,851. These dies represent a significant advance in the die cutting art primarily because they can be manufactured to precise and exact dimensions by automatic, tape controlled machines, thereby eliminating any need for expensive manual operations and making it possible to reproduce exact duplicate dies whenever necessary.
Notwithstanding their obvious advantages over prior methods of making rotary dies, the present EDM dies have several inherent disadvantages. For example, the cutting edges of an average die constitute only about 10% to possibly 20% of the total surface area of the die blank. Consequently, a substantial amount of metal must be machined away from the blank surface in order to create the raised cutting edges. This not only requires a considerable amount of time for the machining operation, but it also results in a substantial amount of metal waste. Furthermore, the die cutting blanks used heretofore are not reusable. In other words, at the end of a production run or when a die becomes worn, it cannot be used to produce another die, but must be scrapped.
The excessive metal wasted during the machining operation coupled with the expense involved with scrapping the used dies constitute significant cost factors which have imposed limitations as to the types of metals which could be economically used for the die blanks.